The present invention generally relates to a micro liquid dispenser of a liquid pillar injector constructed of a liquid storage chamber, an actuator, and an aperture in a semiconductor substrate and a method for operating the dispenser. The invention further relates to a method for depositing liquid on a substrate by a micro liquid dispenser by first forming a liquid pillar and then contacting the tip of the pillar with the substrate such that only part of the liquid pillar is deposited on the substrate while the remaining liquid pillar is withdrawn into the dispenser.
Since the advent of micro liquid dispensers, i.e., specifically for low cost printers for personal computers, a variety of inkjet printing devices have been developed and utilized in the industry. These inkjet printing mechanisms include the piezoelectric type, the electrostatic type and the thermal bubble type, etc. After the first thermal inkjet printer becomes commercially available in the early 1980""s, there has been a great progress in the development of other printing technologies for applications in optoelectronics, biotechnology and biomedical applications.
In an inkjet printer, a liquid droplet injector is used as one of the key mechanisms. To provide a high-quality and reliable inkjet printer, the availability of a liquid droplet injector capable of supplying high-quality droplets at high-frequency and high-spacial resolution is critical.
Presently, there are two types of inkjet printers that are available in the marketplace, the piezoelectric type and the thermal type. The thermal inkjet system, also known as thermal bubble inkjet system, as thermally driven bubble system or as bubble jet system utilizes bubble to eject ink droplets out of an ink supply chamber, while piezoelectric printers utilize piezoelectric actuators to pump ink out from a reservoir chamber. The principle of operation for a thermal bubble inkjet system is that an electrical current is first conducted to the heater by an electrode to boil liquid in an ink reservoir chamber. When the liquid is in a boiling state, bubble forms in the liquid and expands and thus functions as a pump to eject a fixed quantity of liquid from the reservoir chamber through an orifice and then forms into droplets. When the electrical current is turned-off, the bubble generated collapses and liquid refills the chamber by capillary force.
When evaluating the performance of a thermal bubble inkjet system, factors such as droplet ejection frequency, cross-talk between adjacent chambers and the generation of satellite droplets are considered. Two of these performance factors, i.e. the satellite droplets, which degrade the sharpness of the image produced and the cross-talk between adjacent chambers and flow channels which decreases the quality and reliability of the inkjet system are frequently encountered. In order to improve the performance of a thermal bubble inkjet system, these drawbacks must be corrected.
For instance, in a traditional biotechnology micro-array fabrication, the technology of needle array spotting or micro stamping is normally utilized. U.S. Pat. No. 5,551,487 discloses a test slide preparation technique in which a contact-type needle or print head is used. The drawbacks of the systems include difficult waste disposal, time consuming cleaning of the needle or print head, and the large and variable dimensions of the print spot. Subsequently, the technique of inkjet printing is developed as disclosed in U.S. Pat. No. 6,341,840 of a inkjet-type substrate printing technique. While the new technique has the advantages of the non-contact, small specimen usage and fast fabrication speed; the inkjet technique has the drawbacks of requiring a large momentum to dislodge the ink droplets, such that droplets are ejected and fly for a long distance before impacting a substrate. Any deviation in the ejection angle of the droplets leads to a printing location error and thus limiting the printing resolution. Furthermore, the size of the droplets and satellite droplets developed further cause printing spot contamination or overlapping affecting the print quality.
It is therefore an object of the present invention to provide a micro liquid dispenser, particularly related to an inkjet head, that does not have the drawbacks or shortcomings of the conventional inkjet head.
It is another object of the present invention to provide a micro liquid dispenser that incorporates a liquid pillar injector for injecting a liquid pillar toward a substrate.
It is a further object of the present invention to provide a micro liquid dispenser that incorporates a liquid pillar injector constructed by a liquid storage chamber, and actuator and an aperture formed in a semiconductor substrate.
It is another further object of the present invention to provide a micro liquid dispenser that incorporates a liquid pillar injector utilizing a piezoelectric, electrostatic, thermoelastic, electromagnetic, or thermal bubble actuator to eject a pillar of liquid toward a substrate.
It is still another object of the present invention to provide a micro liquid dispenser that incorporates a liquid pillar injector suitable for depositing a liquid that has a viscosity smaller than 1000 poise onto a top surface of a substrate.
It is yet another object of the present invention to provide a method for depositing a liquid on a substrate by utilizing a micro liquid dispenser.
It is still another further object of the present invention to provide a method for depositing liquid on a substrate utilizing a micro liquid dispenser by positioning the substrate juxtaposed to the micro liquid dispenser at a distance smaller than a length of the liquid pillar ejected from the aperture.
It is yet another further object of the present invention to provide a method for depositing liquid on a substrate by a micro liquid dispenser by providing a top surface of the substrate coated with a hydrophillic agent at locations to be covered by the liquid.
In accordance with the present invention, a micro liquid dispenser incorporating a liquid pillar injector and a method for depositing liquid on a substrate by a micro liquid dispenser are disclosed.
In a preferred embodiment, a micro liquid dispenser incorporating a liquid pillar injector can be constructed by a liquid storage chamber for storing a liquid therein; an actuator for initiating a liquid dispensing action; and an aperture for forming a liquid pillar therethrough.
In the micro liquid dispenser, the actuator may be selected from the group consisting of a piezoelectric actuator, an electrostatic actuator, a thermoelastic actuator, an electro-magnetic actuator and a thermal bubble actuator. The micro liquid dispenser further includes a semiconductor substrate onto which the liquid storage chamber, the actuator and the aperture are formed. The micro liquid dispenser may further include a silicon substrate onto which the liquid storage chamber, the actuator and the aperture are formed. The aperture may have a diameter smaller than a diameter of a print spot, or the aperture may have a diameter larger than a diameter of a print spot. The liquid stored in the liquid storage chamber may have a viscosity smaller than 1000 poise.
The present invention is further directed to a method for depositing liquid on a substrate by a micro liquid dispenser which can be carried out by the operating steps of providing a micro liquid dispenser equipped with a liquid storage chamber, an actuator and an aperture; providing a substrate that has a top surface for receiving a liquid; positioning the substrate juxtaposed to the micro liquid dispenser with the top surface of the substrate spaced apart from the aperture at a preset distance; actuating the actuator and injecting a liquid pillar from the aperture toward and until a tip of the liquid pillar contacts the surface of the substrate and thus depositing only partially the liquid pillar on the top surface of the substrate; and stopping said actuator and retracting partially the liquid pillar into the aperture and the liquid storage chamber.
The method for depositing liquid on a substrate by a micro liquid dispenser may further include a step of positioning the substrate juxtaposed to the micro liquid dispenser at a distance smaller than the length of the liquid pillar injected from the aperture. The method may further include the step of filling the liquid storage chamber with a liquid that has a viscosity less than 1000 poise. The method may further include the step of providing the substrate with a top surface selectively coated with a hydrophillic agent at locations to be covered by the liquid; or the step of providing the substrate with a top surface selectively coated with a hydrophobic agent at locations that are not to be covered by the liquid.
The method for depositing liquid on a substrate by a micro liquid dispenser may further include the step of depositing less than 50 vol. % of the total volume of the liquid pillar on the top surface of the substrate, or the step of depositing less than 30 vol. % of the total volume of the liquid pillar on the top surface of the substrate. The method may further include the step of retracting at least 50% of the total volume of the liquid pillar into the aperture and the liquid storage chamber; or the step of retracting at least 70% of the total volume of the liquid pillar into the aperture and the liquid storage chamber. The method may further include the step of providing the substrate with a top surface selectively treated with a hydrophillic agent selected from the group consisting of NH3:H2O:H2O2, H2SO4:H2O2 and polyethylene glycol. The method may further include the step of providing the substrate with a top surface selectively treated with a hydrophobic agent selected from the group consisting of hydrofluoric acid and dichloro-dimethyl-silane. The method may further include the step of providing the substrate having a top surface with a surface porosity of less than 10% of the total surface area.